Thermochromic color-memory composition and thermochromic color-memory microcapsule pigment encapsulating same

ABSTRACT

Provided are thermochromic color-memory composition and thermochromic color-memory microcapsule pigment encapsulating the same, the thermochromic color-memory composition including: (a) a component composed of an electron-donating color-developing organic compound; (b) a component composed of an electron-accepting compound; and (c) a component composed of an ester compound represented by the following Formula (1) as a reaction medium which controls color reaction between the components (a) and (b): 
     
       
         
         
             
             
         
       
     
     (wherein, R represents an alkyl group having 3 to 18 carbon atoms or an aliphatic acyl group having 3 to 18 carbon atoms; X represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 or 2 carbon atoms or a halogen atom; Y represents a hydrogen atom or a methyl group; and Z represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 or 2 carbon atoms or a halogen atom).

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to thermochromic color-memory compositionand thermochromic color-memory microcapsule pigment encapsulating thesame. More particularly, the present invention relates to: thermochromiccolor-memory composition which displays reversible discoloration betweencoloration and decoloration showing prominent hysteresis characteristicsaccording to temperature change and retains either a colored state or adecolored state in an interchangeable and reversible manner even afterremoval of application of heat or cold required for the discoloration;and thermochromic color-memory microcapsule pigment encapsulating thecomposition.

Background Art

The present applicant has previously made proposals on thermochromiccolor-memory materials of this kind (see, for example, Patent Documents1 to 6).

In contrast to reversibly thermochromic materials of a conventional typethat change colors across a discoloration temperature, in which only onespecific state of those states before and after the discoloration exitsin a normal temperature range and the other state is maintained whileheat or cold required for the expression of the specific state is beingapplied but the state in the normal temperature range is restored oncethe application of heat or cold is terminated, the above-mentionedthermochromic color-memory materials not only are capable of selectivelymaintaining either a color at the lower temperature side than thediscoloration temperature or a color at the higher temperature side thanthe discoloration temperature in a normal temperature range but also canbe made to interchangeably maintain these colors by applying theretoheat or cold as required, and such thermochromic color-memory materialshave thus been applied to a wide variety of fields including the fieldsof thermochromic recording materials, toys and printing.

PRIOR ART DOCUMENTS Patent Documents

[Patent Document 1] Japanese Patent Laid-open Publication No. 2005-1369

[Patent Document 2] Japanese Patent Laid-open Publication No.2006-137886

[Patent Document 3] Japanese Patent Laid-open Publication No.2006-188660

[Patent Document 4] Japanese Patent Laid-open Publication No.2008-280523

[Patent Document 5] WO 2010/131684

[Patent Document 6] WO 2012/046837

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The color-memory effect of this kind is expressed in a system where,among compounds selected from esters that control color reaction, aspecific compound is applied as a constituent. The present inventionfurther searches for a compound functioning as a reaction medium whichallows the above-described color-memory effect to be expressed, and anobject of the present invention is to improve the freedom in theselection of a reaction medium and thereby further improve theutilization of such a kind of thermochromic color-memory material.

Means for Solving the Problems

The present inventor discovered that a system where an ester compoundhaving a specific structure is applied as a reaction medium for colorreaction allows prominent thermochromic characteristics with a largehysteresis width (ΔH) to be displayed and an effective color-memoryproperty to be thus expressed, thereby completing the present invention.

The present invention relates to thermochromic color-memory compositioncomprising: (a) a component composed of an electron-donatingcolor-developing organic compound; (b) a component composed of anelectron-accepting compound; and (c) a component composed of an estercompound represented by the following Formula (1) as a reaction mediumwhich controls color reaction between the components (a) and (b):

(wherein, R represents an alkyl group having 3 to 18 carbon atoms or analiphatic acyl group having 3 to 18 carbon atoms; X represents ahydrogen atom, an alkyl group having 1 to 3 carbon atoms, an alkoxygroup having 1 or 2 carbon atoms or a halogen atom; Y represents ahydrogen atom or a methyl group; and Z represents a hydrogen atom, analkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 or 2carbon atoms or a halogen atom).

The present invention also relates to thermochromic color-memorymicrocapsule pigment encapsulating the above-described thermochromiccolor-memory composition.

Effects of the Invention

The thermochromic color-memory microcapsule pigment of the presentinvention induces reversible discoloration between coloration anddecoloration. In this reversible discoloration, the thermochromiccolor-memory microcapsule pigment of the present invention not onlyinduces reversible discoloration between coloration and decoloration,showing a large hysteresis width (ΔH) in terms of colordensity-temperature curve, but also is capable of interchangeablymemorizing and retaining both colors at the lower temperature side andhigher temperature side than the discoloration temperature and isallowed to effectively express a property of reproducing, memorizing andretaining either of these colors in a reversible manner by applyingthereto heat or cold as required. Therefore, according to the presentinvention, thermochromic color-memory composition applicable to variousfields of thermochromic recording materials, toys, ornaments,temperature indication, training and learning elements, printing and thelike, as well as thermochromic color-memory microcapsule pigmentencapsulating the composition can be provided.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph illustrating the hysteresis characteristics of thethermochromic color-memory composition of the present invention in acolor density-temperature curve.

DETAILED DESCRIPTION OF THE INVENTION Mode for Carrying Out theInvention

The hysteresis characteristics of the thermochromic color-memorycomposition of the present invention and thermochromic color-memorymicrocapsule pigment comprising the same (a reversibly thermochromiccomposition having a color-memory property and a reversiblythermochromic microcapsule pigment having a color-memory property whichcomprises the same) will now be described based on the graph representedby the color density-temperature curve of FIG. 1.

In FIG. 1, the color density is plotted on the ordinate and thetemperature is plotted on the abscissa. A change in the color densitydue to temperature change occurs along the arrow. Here, “A” is a pointwhich represents the density at a temperature T₄ at which a completelydecolored state is achieved (hereinafter, referred to as “completedecoloration temperature”); “B” is a point which represents the densityat a temperature T₃ at which a completely colored state can bemaintained (hereinafter, referred to as “decoloration on-settemperature”); “C” is a point which represents the density at atemperature T₂ at which a completely decolored state can be maintained(hereinafter, referred to as “coloration on-set temperature”); and “D”is a point which represents the density at a temperature T₁ at which acompletely colored state is achieved (hereinafter, referred to as“complete coloration temperature”).

The discoloration temperature region is a temperature region between T₁and T₄, and the temperature region between T₂ and T₃ is a substantialdiscoloration temperature region, that is, a temperature region whereeither a colored state or a decolored state can be maintained.

Specifically, a change of the reversibly thermochromic microcapsulepigment from a decolored state to a colored state can be initiated bycooling the pigment to the coloration on-set temperature or lower. Acompletely colored state can be brought about by cooling the pigment tothe complete coloration temperature or lower, and this state can bemaintained unless the temperature of the reversibly thermochromicmicrocapsule pigment is increased to the decoloration on-settemperature.

Further, a change of the reversibly thermochromic microcapsule pigmentfrom a colored state to a decolored state can be initiated by heatingthe pigment to the decoloration on-set temperature or higher withapplication of heat generated by friction or the like. A completelydecolored state can be brought about by heating the pigment to thecomplete decoloration temperature or higher, and this state can bemaintained unless the temperature of the reversibly thermochromicmicrocapsule pigment is decreased to the coloration on-set temperature.

The length of a line segment EF is a scale representing the contrast ofdiscoloration, and the length of a line segment HG is a temperaturewidth representing the degree of hysteresis (hereinafter, the hysteresiswidth is denoted as “ΔH”). The greater the ΔH value, the more easily therespective states before and after discoloration can be maintained. TheΔH value in which the respective states before and after discolorationcan be maintained is 8° C. or greater, specifically in a range of 8° C.to 80° C. Here, Δt, which is a difference between T₄ and T₃ or betweenT₂ and T₁, is a scale representing the sensitivity of the discoloration,and a practical range thereof is preferably 1° C. to 15° C., morepreferably 1° C. to 10° C.

In order to allow only one specific state of those states before andafter discoloration to exist in a normal temperature range, the completedecoloration temperature (T₄) is preferably 40° C. or higher, morepreferably 50° C. or higher, still more preferably 60° C. or higher, andthe coloration on-set temperature (T₂) is preferably 0° C. or lower,more preferably −5° C. or lower, still more preferably −10° C. or lower.

In the present invention, the ratio of the components (a), (b) and (c)varies depending on the color density, discoloration temperature, modeof discoloration and the type of each component; however, generally, asa component ratio at which desired properties are obtained, the ratio ofthe component (b) is in a range of preferably 0.1 to 50 parts, morepreferably 0.5 to 20 parts, and that of the component (c) is in a rangeof preferably 1 to 800 parts, more preferably 5 to 200 parts, withrespect to 1 part of the component (a) (these ratios are all based onmass).

In addition, a combination of two or more compounds may be used as eachcomponent and, for example, an antioxidant, an ultraviolet absorber, aninfrared absorber and/or a solubilizing aid can be added to eachcomponent within a range where its functions are not impaired.

Specific compounds of the respective components (a), (b) and (c) will beexemplified below.

Examples of the component (a) of the present invention, namelyelectron-donating color-developing organic compound, include phthalidecompounds, fluoran compounds, styrylquinoline compounds, diazarhodaminelactone compounds, pyridine compounds, quinazoline compounds andbisquinazoline compounds, among which phthalide compounds and fluorancompounds are preferred. Examples of the phthalide compounds includediphenylmethane phthalide compounds, phenylindolyl phthalide compounds,indolyl phthalide compounds, diphenylmethane azaphthalide compounds,phenylindolyl azaphthalide compounds and derivatives of these compounds,among which phenylindolyl azaphthalide compounds and their derivativesare preferred. Examples of the fluoran compounds include aminofluorancompounds, alkoxyfluoran compounds, and derivatives of these compounds.

Examples of the electron-donating color-developing organic compoundinclude the followings:

-   3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide,-   3-(4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)phthalide,-   3,3-bis(1-n-butyl-2-methylindol-3-yl)phthalide,-   3,3-bis(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide,-   3-[2-ethoxy-4-(N-ethylanilino)phenyl]-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide,-   3,6-diphenylaminofluoran,-   3,6-dimethoxyfluoran,-   3,6-di-n-butoxyfluoran,-   2-methyl-6-(N-ethyl-N-p-tolylamino)fluoran,-   3-chloro-6-cyclohexylaminofluoran,-   2-methyl-6-cyclohexylaminofluoran,-   2-(2-chloroamino)-6-dibutylaminofluoran,-   2-(2-chloroanilino)-6-di-n-butylaminofluoran,-   2-(3-trifluoromethylanilino)-6-diethylaminofluoran,-   2-(N-methylanilino)-6-(N-ethyl-N-p-tolylamino)fluoran,-   1,3-dimethyl-6-diethylaminofluoran,-   2-chloro-3-methyl-6-diethylaminofluoran,-   2-anilino-3-methyl-6-diethylaminofluoran,-   2-anilino-3-methoxy-6-diethylaminofluoran,-   2-anilino-3-methyl-6-di-n-butylaminofluoran,-   2-anilino-3-methoxy-6-di-n-butylaminofluoran,-   2-xylidino-3-methyl-6-diethylaminofluoran,-   1,2-benz-6-diethylaminofluoran,-   1,2-benz-6-(N-ethyl-N-isobutylamino)fluoran,-   1,2-benz-6-(N-ethyl-N-isoamylamino)fluoran,-   2-(3-methoxy-4-dodecoxystyryl)quinoline,-   spiro[5H-(1)benzopyrano(2,3-d)pyrimidine-5,1′(3′H)isobenzofuran]-3′-one,-   2-(diethylamino)-8-(diethylamino)-4-methyl-spiro[5H-(1)benzopyrano(2,3-g)pyrimidine-5,1′(3′H)isobenzofuran]-3-one,-   2-(di-n-butylamino)-8-(di-n-butylamino)-4-methyl-spiro[5H-(1)benzopyrano(2,3-g)pyrimidine-5,1′(3′H)isobenzofuran]-3-one,-   2-(di-n-butylamino)-8-(diethylamino)-4-methyl-spiro[5H-(1)benzopyrano(2,3-g)pyrimidine-5,1′(3′H)isobenzofuran]-3-one,-   2-(di-n-butylamino)-8-(N-ethyl-N-i-amylamino)-4-methyl-spiro[5H-(1)benzopyrano(2,3-g)pyrimidine-5,1′(3′H)isobenzofuran]-3-one,-   2-(dibutylamino)-8-(dipentylamino)-4-methyl-spiro[5H-(1)benzopyrano(2,3-g)pyrimidine-5,1′(3′H)-isobenzofuran]-3-one,-   3-(2-methoxy-4-dimethylaminophenyl)-3-(1-butyl-2-methylindol-3-yl)-4,5,6,7-tetrachlorophthalide,-   3-(2-ethoxy-4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)-4,5,6,7-tetrachlorophthalide,-   3-(2-ethoxy-4-diethylaminophenyl)-3-(1-pentyl-2-methylindol-3-yl)-4,5,6,7-tetrachlorophthalide,-   4,5,6,7-tetrachloro-3-[4-(dimethylamino)-2-methylphenyl]-3-(1-ethyl-2-methyl-1H-indol-3-yl)-1(3H)-isobenzofuranone,-   3′,6′-bis[phenyl(2-methylphenyl)amino]-spiro[isobenzofuran-1(3H),9′-[9H]xanthen]-3-one,-   3′,6′-bis[phenyl(3-methylphenyl)amino]-spiro[isobenzofuran-1(3H),9′-[9H]xanthen]-3-one,-   3′,6′-bis[phenyl(3-ethylphenyl)amino]-spiro[isobenzofuran-1(3H),9′-[9H]xanthen]-3-one,-   4-[2,6-bis(2-ethoxyphenyl)-4-pyridinyl]-N,N-dimethylbenzenamine,-   2-(4′-dimethylaminophenyl)-4-methoxy-quinazoline, and-   4,4′-(ethylenedioxy)-bis[2-(4-diethylaminophenyl)quinazoline]

In addition to the above-mentioned compounds containing a substituent(s)in a xanthene ring-forming phenyl group, the fluoran compounds may alsobe compounds which contain a substituent in a xanthene ring-formingphenyl group as well as a substituent in a lactone ring-forming phenylgroup (these substituents may be, for example, an alkyl group such as amethyl group or a halogen atom such as a chloro group).

Examples of the component (b), that is, an electron-accepting compound,include active proton-containing compounds; pseudo-acidic compounds(compounds which are not acids but each act as an acid in thecomposition to cause the component (a) to develop a color); and electronhole-containing compounds.

Examples of the active proton-containing compounds include phenolichydroxyl group-containing compounds and metal salts thereof; carboxylicacids and metal salts thereof, preferably aromatic carboxylic acids,aliphatic carboxylic acids having 2 to 5 carbon atoms, and metal saltsthereof; acidic phosphoric acid esters and metal salts thereof; andazole-based compounds and derivatives thereof, preferably 1,2,3-triazoleand derivatives thereof. Thereamong, phenolic hydroxyl group-containingcompounds are preferred since they can allow effective thermaldiscoloration characteristics to be expressed. The phenolic hydroxylgroup-containing compounds widely include monophenol compounds andpolyphenol compounds, and bis-type and tris-type phenols,phenol-aldehyde condensation resins and the like are also includedtherein. Among the phenolic hydroxyl group-containing compounds, thosewhich contain at least two benzene rings or have a bis-hydroxyphenylsulfide structure are preferred. Further, these compounds may also havea substituent, examples of which include an alkyl group, an aryl group,an acyl group, an alkoxycarbonyl group, a carboxy group and an esterthereof, as well as an amide group and a halogen group. Further, whenthe active proton-containing compounds are metal salts, the metalcontained therein is, for example, sodium, potassium, calcium, zinc,zirconium, aluminum, magnesium, nickel, cobalt, tin, copper, iron,vanadium, titanium, lead or molybdenum. Examples of the phenolichydroxyl group-containing compounds include monophenol compounds andpolyphenol compounds, as well as phenolic hydroxyl group-containingcompounds having a substituent, such as an alkyl group, an aryl group,an acyl group, an alkoxycarbonyl group, a carboxy group or an esterthereof, an amide group or a halogen group; bis-type and tris-typephenols; and phenol-aldehyde condensation resins. Further, the activeproton-containing compounds may also be metal salts of these phenolichydroxyl group-containing compounds.

Specific examples of the phenolic hydroxyl group-containing compoundsinclude the followings:

-   -   phenol, o-cresol, tert-butyl catechol, nonylphenol,        n-octylphenol, n-dodecylphenol, n-stearylphenol, p-chlorophenol,        p-bromophenol, o-phenylphenol, n-butyl-p-hydroxybenzoate,        n-octyl-p-hydroxybenzoate, resorcin, dodecyl gallate,        4,4-dihydroxydiphenylsulfone, bis(4-hydroxyphenyl)sulfide,        1,1-bis(4-hydroxyphenyl)ethane, 1,1-bis(4-hydroxyphenyl)propane,        1,1-bis(4-hydroxyphenyl)-n-butane,        1,1-bis(4-hydroxyphenyl)n-pentane,        1,1-bis(4-hydroxyphenyl)-n-hexane,        1,1-bis(4-hydroxyphenyl)-n-heptane,        1,1-bis(4-hydroxyphenyl)-n-octane,        1,1-bis(4-hydroxyphenyl)-n-nonane,        1,1-bis(4-hydroxyphenyl)-n-decane,        1,1-bis(4-hydroxyphenyl)-n-dodecane,        1,1-bis(4-hydroxyphenyl)-2-methylpropane,        1,1-bis(4-hydroxyphenyl)-3-methylbutane,        1,1-bis(4-hydroxyphenyl)-3-methylpentane,        1,1-bis(4-hydroxyphenyl)-2,3-dimethylpentane,        1,1-bis(4-hydroxyphenyl)-2-ethylbutane,        1,1-bis(4-hydroxyphenyl)-2-ethylhexane,        1,1-bis(4-hydroxyphenyl)-3,7-dimethyloctane,        1-phenyl-1,1-bis(4-hydroxyphenyl)ethane,        2,2-bis(4-hydroxyphenyl)propane,        2,2-bis(4-hydroxyphenyl)-n-butane,        2,2-bis(4-hydroxyphenyl)-n-pentane,        2,2-bis(4-hydroxyphenyl)-n-hexane,        2,2-bis(4-hydroxyphenyl)-n-heptane,        2,2-bis(4-hydroxyphenyl)-n-octane,        2,2-bis(4-hydroxyphenyl)-n-nonane,        2,2-bis(4-hydroxyphenyl)-n-decane,        2,2-bis(4-hydroxyphenyl)-n-dodecane,        2,2-bis(4-hydroxyphenyl)ethyl propionate,        2,2-bis(4-hydroxyphenyl)-4-methylpentane,        2,2-bis(4-hydroxyphenyl)-4-methylhexane,        2,2-bis(4-hydroxyphenyl)hexafluoropropane, and        2,2-bis(4-hydroxy-3-methylphenyl)propane

The component (c) functions as a reaction medium which controls colorreaction between the components (a) and (b).

The component (c) used in the present invention is an ester compoundrepresented by the following Formula (1), which can be obtained by, forexample, a reaction between an alkoxy benzoic acid and phenoxyethanol orphenoxypropanol:

In the Formula (1),

R represents an alkyl group having 3 to 18 carbon atoms or an aliphaticacyl group having 3 to 18 carbon atoms, preferably an alkyl group having4 to 14 carbon atoms or an aliphatic acyl group having 6 to 16 carbonatoms, more preferably an alkyl group having 4 to 12 carbon atoms or analiphatic acyl group having 8 to 14 carbon atoms;

X represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms,an alkoxy group having 1 or 2 carbon atoms or a halogen atom, preferablya hydrogen atom, a methyl group or a methoxy group;

Y represents a hydrogen atom or a methyl group, preferably a hydrogenatom; and

Z represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms,an alkoxy group having 1 or 2 carbon atoms or a halogen atom, preferablya hydrogen atom, a methyl group or a methoxy group, more preferably ahydrogen atom.

Specific examples of the ester compound represented by the Formula (1)are shown below.

The above-exemplified ester compounds are capable of achieving a broadhysteresis width comparable to that of an ester compound used inconventional thermochromic color-memory compositions and have anexcellent function of selectively maintaining either a color at thelower temperature side than the discoloration temperature or a color atthe higher temperature side than the discoloration temperature;therefore, these ester compounds have excellent applicability to variousapplications.

In the composition of the present invention, two or more components (c)having different structures can be used in combination. In addition,other esters, alcohols, carboxylic acids, ketones, amides and the likecan also be used in combination and, when a combination of components(c) is used, particularly, esters having similar chemical properties arepreferably used in combination.

The three components (a), (b) and (c) can also be encapsulated in amicrocapsule to form thermochromic color-memory microcapsule pigment. Byprotecting these components with a capsule membrane wall, needless tosay, their functions are not deteriorated even if the components arebrought into contact with a chemically active substance such as anacidic substance, a basic substance or a peroxide or with other solventcomponent, and the heat stability can also be improved.

Further, the microcapsule pigment can be put into practical use afterforming a secondary resin coating film on the surface thereof inaccordance with the intended use so as to impart the microcapsulepigment with durability or to modify the surface properties.

The average particle size of the microcapsule pigment is preferably 0.1to 50 μm, more preferably 0.1 to 30 μm, still more preferably 0.5 to 20μm and, by controlling the average particle size of the microcapsulepigment in this range, the practicality of the microcapsule pigment isimproved.

The average particle size and the particle size distribution aremeasured using, for example, a laser diffraction/scattering-typeparticle size distribution analyzer [manufactured by Horiba, Ltd.;LA-300], and the average particle size (median diameter) can becalculated based on volume from the thus measured values.

When the microcapsule pigment has an average particle size of 50 μm orsmaller, its dispersion stability and processing suitability can bemaintained when the microcapsule pigment is blended into an ink, a paintor a thermoplastic resin.

Meanwhile, at an average particle size of 0.1 μm or larger, themicrocapsule pigment can exhibit high-density color developingproperties.

Further, by making the microcapsule pigment into fine particles, the ΔHvalue thereof can be made larger than that of a case where themicrocapsule pigment is not in the form of fine particles.

The ratio of the contents constituting the microcapsule pigment and themembrane wall (contents:membrane wall) is effectively in a range of 7:1to 1:1 (mass ratio) and, by controlling the ratio of the contents andthe membrane wall in this range, reduction in the color density andclarity during color development can be inhibited. The ratio of thecontents and the membrane wall (contents:membrane wall) is preferably6:1 to 1:1 (mass ratio).

Examples of a microencapsulation method include conventionally knownmethods such as interfacial polymerization using an isocyanate, in situpolymerization of a melamine-formalin system or the like, submergedcuring and coating, phase separation from an aqueous solution, phaseseparation from an organic solvent, melt-dispersion and cooling, gaseoussuspension and coating, and spray-drying, and the microencapsulationmethod is selected as appropriate in accordance with the intended use.

In the microcapsule pigment, a conventional dye or pigment(non-thermochromic one) can also be incorporated so as to allow themicrocapsule pigment to exhibit a discoloration behavior from a color(1) to a color (2).

As required, the thermochromic color-memory microcapsule pigment can bedispersed in a vehicle containing an additive(s) to prepare a liquidthermochromic color-memory composition. Specific examples of such acomposition include (i) printing inks used in screen printing, offsetprinting, process printing, gravure printing, coater printing, padprinting or the like; (ii) paints used in brush coating, spray coating,electrostatic coating, electrodeposition coating, flow coating, rollercoating, dip coating or the like; (iii) inks for writing instrumentssuch as marking pens, ballpoint pens, fountain pens and brush pens; (iv)inks for coating tools; (v) painting colors; (vi) cosmetics; and (vii)coloring liquids for fibers.

In one embodiment, the liquid thermochromic color-memory composition cancontain the thermochromic color-memory microcapsule pigment in an amountof preferably 5 to 40% by mass, more preferably 10 to 40% by mass, stillmore preferably 10 to 30% by mass, with respect to the total mass of theliquid thermochromic color-memory composition. By controlling the amountof the microcapsule pigment in this range, a desirable color developmentdensity can be achieved and deterioration of the ink outflow propertiescan be inhibited.

Examples of the additive include resins, cross-linking agents, curingagents, desiccants, plasticizers, viscosity-adjusting agents,dispersants, ultraviolet absorbers, antioxidants, light stabilizers,anti-settling agents, lubricants, gelling agents, antifoaming agents,delustering agents, penetrating agents, pH regulators, foaming agents,coupling agents, humectants, antifungal agents, preservatives andanticorrosives.

Example of the vehicle include oil-based vehicles containing an organicsolvent; and aqueous vehicles containing water and, as required, anorganic solvent.

Examples of the organic solvent include ethanol, propanol, butanol,glycerin, sorbitol, triethanolamine, diethanolamine, monoethanolamine,ethylene glycol, diethylene glycol, thiodiethylene glycol, polyethyleneglycol, propylene glycol, butylene glycol, ethylene glycol monomethylether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether,diethylene glycol monomethyl ether, diethylene glycol monoethyl ether,diethylene glycol monobutyl ether, propylene glycol monobutyl ether,ethylene glycol monomethyl ether acetate, sulfolane, 2-pyrrolidone andN-methyl-2-pyrrolidone.

Examples of an ink composition for writing instruments includeshear-thinning ink compositions containing a shear-thinning agent in avehicle; and cohesive ink compositions containing an aqueous polymericcoagulant in a vehicle, in which a pigment is suspended in a looselyaggregated state.

By incorporating the shear-thinning agent, not only aggregation andsedimentation of the pigment but also bleeding of handwriting can beinhibited, so that good handwriting can be made. Further, in cases wherethe ink composition is filled into a ballpoint pen, leakage of the inkfrom a gap between a ball and a tip can be inhibited when the pen is notin use, and backflow of the ink composition can be inhibited when thepen is left with the writing end facing upward (in an upright state).

Examples of the shear-thinning agent include xanthan gum; welan gum;succinoglycans (average molecular weight: about 1,000,000 to 8,000,000),which are organic acid-modified hetero-polysaccharides comprisingglucose and galactose as constituting monosaccharides; guar gum; locustbean gum and derivatives thereof; hydroxyethyl cellulose; alkyl alginateesters; polymers containing an alkyl ester of methacrylic acid as a maincomponent and having a weight-average molecular weight of 100,000 to150,000; glucomannan; thickening polysaccharides which have a gelationability and are extracted from seaweeds, such as agar or carrageenin;benzylidene sorbitol, benzylidene xylitol, and derivatives thereof;cross-linkable acrylic acid polymers; inorganic fine particles; nonionicsurfactants having an HLB value of 8 to 12, such as polyglycerin fattyacid esters, polyoxyethylene sorbitan fatty acid esters, polyethyleneglycol fatty acid esters, polyoxyethylene alkyl ethers, polyoxypropylenealkyl ethers, polyoxyethylene alkylphenyl ethers and fatty acid amides;salts of dialkyl or dialkenyl sulfosuccinic acids; mixtures ofN-alkyl-2-pyrrolidone and an anionic surfactant; and mixtures of apolyvinyl alcohol and an acrylic resin.

Examples of the aqueous polymeric coagulant includepolyvinylpyrrolidones, polyethylene oxides and aqueous polysaccharides.

Examples of the aqueous polysaccharides include tragacanth gum, guargum, pullulan, cyclodextrin and aqueous cellulose derivatives, andspecific examples of the aqueous cellulose derivatives include methylcellulose, hydroxyethyl cellulose, hydroxypropyl cellulose,hydroxyethylmethyl cellulose and hydroxypropylmethyl cellulose.

By using a comb-type polymeric dispersant containing carboxyl groups inside chains and an organic nitrogen sulfur compound in combination withthe polymeric coagulant, the dispersibility of loose aggregates of themicrocapsule pigment formed by the action of the polymeric coagulant canbe improved.

The comb-type polymeric dispersant containing carboxyl groups in sidechains is not particularly restricted as long as it is a comb-typepolymeric compound having a plurality of carboxyl groups in side chains,and it is preferably an acrylic polymer compound having a plurality ofcarboxyl groups in side chains, examples of which include SOLSPERSE43000 (trade name) manufactured by Lubrizol Japan Ltd.

The organic nitrogen sulfur compound further inhibits the sedimentationof the microcapsule pigment caused by vibration when the ink compositionis filled in a writing instrument for practical use. This is because theorganic nitrogen sulfur compound further improves the dispersibility ofthe loose aggregates of the microcapsule pigment by the action of thecomb-type polymeric dispersant containing carboxyl groups in sidechains.

As the organic nitrogen sulfur compound, a compound selected fromthiazole-based compounds, isothiazole-based compounds,benzothiazole-based compounds and benzisothiazole-based compounds isused.

As the organic nitrogen sulfur compound, specifically, one or morecompounds selected from 2-(4-thiazoyl)-benzimidazole (TBZ),2-(thiocyanatemethylthio)-1,3-benzothiazol (TCMTB),2-methyl-4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-oneare used and, preferably, one or more compounds selected from2-(4-thiazoyl)-benzimidazole (TBZ), 2-methyl-4-isothiazolin-3-one and5-chloro-2-methyl-4-isothiazolin-3-one are used.

Examples of the organic nitrogen sulfur compound include TOPSIDE 88,TOPSIDE 133, TOPSIDE 170, TOPSIDE 220, TOPSIDE 288, TOPSIDE 300, TOPSIDE400, TOPSIDE 500, TOPSIDE 600, TOPSIDE 700Z, TOPSIDE 800 and TOPSIDE 950(trade names), which are manufactured by Permachem Asia Ltd.; andHOKUSTAR HP, HOKUSTAR E50A, HOKUSIDE P200, HOKUSIDE 6500, HOKUSIDE 7400,HOKUSIDE MC, HOKUSIDE 369 and HOKUSIDE R-150 (trade names), which aremanufactured by Hokko Sangyo, Co., Ltd.

The mass ratio of the comb-type polymeric dispersant containing carboxylgroups in side chains and the organic nitrogen sulfur compound ispreferably 1:1 to 1:10, more preferably 1:1 to 1:5. By satisfying thisrange, the dispersibility of the loose aggregates of the microcapsulepigment and inhibition of the sedimentation of the microcapsule pigmentcaused by vibration can be sufficiently exhibited.

Further, by adding an aqueous resin, handwriting with the pigment can beimparted with fixability on paper surface and viscosity. This aqueousresin composition also has a function of further improving the stabilityof the microcapsule pigment in an ink composition which contains thecomb-type polymeric dispersant having carboxyl groups in side chains andthe organic nitrogen sulfur compound.

Examples of the aqueous resin include alkyd resins, acryl resins,styrene-maleic acid copolymers, cellulose derivatives,polyvinylpyrrolidones, polyvinyl alcohols and dextrin, among which apolyvinyl alcohol is preferably used.

Among polyvinyl alcohols, a partially saponified polyvinyl alcoholhaving a saponification degree of 70 to 89% by mol is more preferablyused since it allows the ink composition to have excellent solubilityeven in an acidic pH range.

As for the amount of the aqueous resin to be added, it is added to theink composition in a range of preferably 0.3 to 3.0% by mass, morepreferably 0.5 to 1.5% by mass.

In cases where the ink composition is filled into a ballpoint pen, it ispreferred to prevent abrasion of the ball-receiving base by adding alubricant, examples of which include higher fatty acids such as oleicacid; nonionic surfactants having a long-chain alkyl group;polyether-modified silicone oils; thiophosphorous acid triesters such astri(alkoxycarbonylmethylester) thiophosphite andtri(alkoxycarbonylethylester) thiophosphite; phosphomonoesters ofpolyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether;phosphodiesters of polyoxyethylene alkyl ether or polyoxyethylenealkylaryl ether; and metal salts, ammonium salts, amine salts andalkanolamine salts thereof.

Further, by incorporating 2,5-dimercapto-1,3,4-thiadiazole and/or a saltthereof, even when the pH of the ink composition is in an acidic oralkaline range, not only defective dispersion and aggregation of themicrocapsule pigment which occur after the once-frozen ink compositionis thawed again can be suppressed and an increase in the viscosity ofthe ink composition and its accompanying blurring and color-fading ofhandwriting can be inhibited, but also, when the ink composition is usedin a ballpoint pen, corrosion of the ball can be inhibited.

In addition, if necessary, (i) a resin for imparting handwriting withfixability to paper surface and viscosity, such as an acryl resin, astyrene-maleic acid copolymer, a cellulose derivative,polyvinylpyrrolidone, polyvinyl alcohol or dextrin; (ii) a pH regulator,for example, an inorganic salt such as sodium carbonate, sodiumphosphate or sodium acetate or an organic basic compound such as anaqueous amine compound; (iii) an anticorrosive such as benzotriazole,tolyltriazole, dicyclohexylammonium nitrite, diisopropylammonium nitriteor saponin; (iv) a preservative or an antifungal agent, such as carbolicacid, sodium salt of 1,2-benzthiazolin-3-one, sodium benzoate, sodiumdehydroacetate, potassium sorbate, paraoxypropylbenzoate or2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine; (v) a wetting agent suchas urea, a non-ionic surfactant, a reduced or non-reduced starchhydrolysate, an oligosaccharide (e.g. trehalose), sucrose, cyclodextrin,glucose, dextrin, sorbitol, mannitol or sodium pyrophosphate; (vi) anantifoaming agent; (vii) a dispersant; and/or (viii) afluorine-containing or non-ionic surfactant for improving thepermeability of the ink composition may also be added to the inkcomposition.

A writing instrument in which the ink composition is stored will now bedescribed. In one embodiment, the writing instrument comprises: an axialbarrel which stores the ink composition; and a pen body which deliversthe ink composition from the axial barrel. Examples of the pen bodyinclude a marking pen body, a ballpoint pen body and a brush pen body.Examples of the marking pen body include marking tips such as fibertips, felt tips and plastic tips. Examples of the ballpoint pen bodyinclude ballpoint pen tips. Examples of the brush pen body include fiberbundles in which fibers are tightly bundled with each other along thelongitudinal direction; plastic porous articles having continuous pores;heat-fused or resin-processed articles of synthetic resin fibers; andextrusion-molded articles of a soft resin or an elastomer.

The use of the ink composition in a ballpoint pen or a marking pen willnow be described in more detail.

In cases where the ink composition is filled into a ballpoint pen, thestructure and shape of the ballpoint pen itself are not particularlyrestricted, and examples thereof include a ballpoint pen in which aballpoint pen refill is housed inside an axial barrel, in whichballpoint pen refill a ballpoint pen tip fitted with a ball is connectedto one end of an ink-storing tube filled with a shear-thinning inkcomposition and an ink follower composition (liquid plug) is in closecontact with the end surface of the ink composition.

As the ballpoint pen tip, for example, a tip holding a ball in aball-holding section formed by press-deforming the vicinity of an end ofa metal pipe inwardly from outside; a tip holing a ball in aball-holding section formed by cutting a metal material using a drill orthe like; a tip made of a metal or plastic, in which a ball-receivingbase made of a resin is arranged; or a tip in which a ball held thereinis pressed forward by a spring can be suitably used.

As the ball, one which is made of cemented carbide, stainless steel,ruby, ceramic, resin, rubber or the like and has a diameter ofpreferably 0.3 to 2.0 mm, more preferably 0.3 to 1.5 mm, still morepreferably 0.3 to 1.0 mm or so can be suitably used.

As the ink-storing tube which stores the ink composition, for example, amolded article made of a thermoplastic resin such as polyethylene,polypropylene, polyethylene terephthalate or nylon or a metal tube canbe used.

The ink-storing tube may be directly connected with the tip, or theink-storing tube may be connected with the tip via a connection member.

Further, examples of the ballpoint pen also include a ballpoint pen inwhich a shear-thinning ink composition is filled into an axial barrelfitted with a ballpoint pen tip at one end directly or via a connectionmember and an ink follower composition is in close contact with the endsurface of the ink composition.

The ballpoint pen may be one which is equipped with a cap covering theballpoint pen tip, or a retractable ballpoint pen with no cap.

The structure and shape of the retractable ballpoint pen are notparticularly restricted, and the ballpoint pen refill can take any shapeas long as it has a structure in which a ballpoint pen refill is housedinside an axial barrel with the writing end arranged on the ballpointpen refill being exposed to the outside air and the writing end isprojected from an opening of the axial barrel by the action of aprojection-retraction mechanism.

Retractable ball point pens can be classified into, for example,knock-type ballpoint pens, rotation-type ballpoint pens and slide-typeballpoint pens.

The knock-type ballpoint pens can take, for example, a configuration inwhich a knocking part is arranged on the rear end or side of the axialbarrel and the ballpoint pen tip is projected from the front-end openingof the axial barrel by pushing the knocking part, or a configuration inwhich the ballpoint pen tip is projected from the front-end opening ofthe axial barrel by pushing a clip arranged on the axial barrel.

The rotation-type ballpoint pens can take, for example, a configurationin which a rotary part is arranged on a rear part of the axial barreland the ballpoint pen tip is projected and retracted through thefront-end opening of the axial barrel by rotating the rotary part.

The slide-type ballpoint pens can take, for example, a configuration inwhich a slide is arranged on the side of the axial barrel and theballpoint pen tip is projected and retracted through the front-endopening of the axial barrel by operating the slide, or a configurationin which the ballpoint pen tip is projected and retracted through thefront-end opening of the axial barrel by sliding a clip arranged on theaxial barrel.

The retractable ballpoint pens may be of a complex type in which aplurality of ballpoint pen refills are stored in the axial barrel andthe writing end of any one of the ballpoint pen refills is projected andretracted through the front-end opening of the axial barrel by theaction of a projection-retraction mechanism.

The ink follower composition which is added to the rear end of the inkcomposition filled in the ballpoint pen refill will now be described.

The ink follower composition comprises a non-volatile liquid or a hardlyvolatile liquid.

Specific examples thereof include vaseline, spindle oil, castor oil,olive oil, refined mineral oil, liquid paraffin, polybutene, α-olefins,oligomers and co-oligomers of α-olefins, dimethyl silicone oil,methylphenyl silicone oil, amino-modified silicone oil,polyether-modified silicone oil, and fatty acid-modified silicone oil.These may be used individually, or two or more thereof may be used incombination.

It is preferred that the viscosity of the non-volatile liquid and/orhardly volatile liquid be increased to an appropriate level by addingthereto a thickening agent. Examples of the thickening agent includesilica having a hydrophobized surface; particulate silica having amethylated surface; aluminum silicate; swellable mica; clay-basedthickening agents such as hydrophobized bentonite and montmorillonite;fatty acid metal soaps such as magnesium stearate, calcium stearate,aluminum stearate and zinc stearate; tribenzylidene sorbitol; fatty acidamides; amide-modified polyethylene wax; hydrogenated castor oil;dextrin compounds such as fatty acid dextrin; and cellulose compounds.

Further, the liquid ink follower composition may also be used incombination with a solid ink follower.

In cases where the ink composition is filled into a marking pen, thestructure and shape of the marking pen itself are not particularlyrestricted, and examples thereof include a marking pen in which an inkabsorbent composed of a fiber bundle is installed in an axial barrel, amarking pen tip composed of a fiber processed body having capillary gapsformed therein is fitted on the axial barrel directly or via aconnection member, and a cohesive ink composition is impregnated intothe ink absorbent of the marking pen formed by connecting the inkabsorbent and the tip; and a marking pen in which a tip and anink-storing tube are arranged via a valve which is opened by pushing thetip and an ink composition is directly stored in the ink-storing tube.

The tip is a conventionally and widely used porous member havingcommunicating pores whose porosity is selected to be in a range of about30 to 70% and which is made of resin-processed fibers, a fused materialof heat-melting fibers, a felt or the like, and one end of the tip isgenerally processed into a shape conforming to the intended purpose,such as a cannonball shape, a rectangular shape or a chisel shape,before being put into practical use.

The ink absorbent is obtained by bundling crimped fibers in thelongitudinal direction and configured such that it is provided in acovering material such as a plastic cylinder or a film and the porosityis adjusted to be in a range of about 40% to 90%.

As the valve, a conventionally and widely used pump-type valve can beused; however, a valve whose spring pressure is set such that the valvecan be push-opened by writing pressure is preferred.

Further, the form of the ballpoint pen and that of the marking pen arenot restricted to the above-described ones, and the writing instrumentmay be of a double-headed type which is fitted with tips of differentforms or with pen tips delivering ink compositions of different colors.

A handwriting produced by writing on a writing surface using a writinginstrument containing the ink composition is allowed to change its colorby the work of a heating tool or cooling tool.

As the heating tool, for example, an electro-heating discolorationdevice equipped with a resistance heating element, a heatingdiscoloration device loaded with hot water or the like, or a hair dryercan be suitably used; however, a friction member is preferably used as ameans which enables discoloration by a simple method.

The friction member is preferably an elastic material such as anelastomer or foamed plastic, which has excellent elasticity and iscapable of generating appropriate friction when rubbed and therebyproducing frictional heat. Particularly, an elastic material that is notabraded by rubbing is preferred.

A handwriting can also be rubbed with an ordinary rubber eraser used forerasing handwriting with a pencil; however, since eraser crumbs aregenerated by the rubbing, the above-described friction member whichhardly generates such crumbs is preferably used.

As the material of the friction member, for example, a silicone resin,an SEBS resin (styrene-ethylene-butadiene-styrene block copolymer) or apolyester resin is used.

The friction member can be combined with a writing instrument and othermember having an arbitrary shape (friction body) to obtain a writinginstrument set, and excellent portability is attained by arranging thefriction member on the writing instrument.

In the case of a writing instrument equipped with a cap, the position atwhich the friction member is arranged is not particularly restricted.For example, the cap itself can be formed by the friction member; theaxial barrel itself can be formed by the friction member; when a clip isarranged, the clip itself can be formed by the friction member; or thefriction member can be arranged on the front end (crown) of the cap orthe rear end of the axial barrel (the part where a writing end is notarranged).

In the case of a retractable writing instrument as well, the position atwhich the friction member is arranged is not particularly restricted.For example, the axial barrel itself can be formed by the frictionmember; when a clip is arranged, the clip itself can be formed by thefriction member; or the friction member can be arranged in the vicinityof an opening of the axial barrel, on the rear end of the axial barrel(the part where a writing end is not arranged), or on the knocking part.

As the cooling tool, for example, a cryogenic discoloration deviceutilizing a Peltier element, a cryogenic discoloration device loadedwith a refrigerant such as cold water or crushed ice, a refrigerator ora freezer can be suitably used.

The liquid thermochromic color-memory composition can be coated orprinted to form a laminate. In this case, the material of a supporttherefor is not restricted and any material is effective. Examplesthereof include paper, synthetic papers, fibers, fabrics, syntheticleathers, leathers, plastics, glass, ceramics, metals, wood and stone.The shape of the support is not restricted to a planar shape, and thesupport may be in an irregular shape.

By arranging a reversibly thermochromic layer containing thethermochromic color-memory composition on the support, a laminate(printed article) can be obtained.

In cases where a non-thermochromic colored layer (including an image)has been formed on the support in advance, the colored layer can be madevisible or invisible depending on temperature change by applying theretoa reversibly thermochromic layer, and this enables to further diversifythe mode of change.

Further, the above-described thermochromic color-memory microcapsulepigment can also be melt-blended with a thermoplastic resin,thermosetting resin, wax or the like into the form of a pellet, powderor paste and utilized as a resin composition for thermochromiccolor-memory molded article. By a widely used means such as injectionmolding, extrusion molding, blow molding or cast molding, a moldedarticle in the form of a three-dimensional article of an arbitraryshape, film, sheet, plate, filament, rod, pipe or the like can beobtained.

Moreover, a pencil core or a crayon can also be obtained bymelt-blending the thermochromic color-memory microcapsule pigment into athermoplastic resin or wax.

By laminating a layer containing a light stabilizer and/or a transparentmetallic luster pigment on a molded article obtained by molding thelaminate or resin composition, the light resistance of the moldedarticle can be improved, or the durability can be improved by arranginga topcoat layer thereon.

Examples of the light stabilizer include ultraviolet absorbers,antioxidants, singlet oxygen quenchers, superoxide anion quenchers andozone quenchers.

Examples of the transparent metallic luster pigment include pigmentsprepared by coating the surface of a core substance, such as naturalmica, synthetic mica, glass piece, alumina or transparent film piece,with a metal oxide such as titanium oxide.

Specific examples of a product comprising the thermochromic color-memorycomposition, the thermochromic color-memory microcapsule pigmentencapsulating the same and the ink composition are listed below.

(1) Toys:

dolls and animal-figured toys; hair of dolls and animal-figured toys;dollhouses and furnitures thereof; doll accessories such as clothes,hats, bags and shoes; accessory toys; stuffed dolls and animals;painting toys; illustrated books for toys; puzzle toys such as jigsawpuzzles; toy bricks; block toys; clay toys; fluid toys; spinning tops;kites; musical toys; cooking toys; gun toys; capturing toys; backgroundtoys; toys imitating vehicles, animals, plants, buildings and foodarticles; and the like

(2) Clothings:

outerwears such as T-shirts, sweaters, blouses, dresses, swimsuits,raincoats and ski wears; footwears such as shoes and shoelaces; personaleffects made of cloth, such as handkerchiefs, towels and wrappingcloths; gloves; neckties; hats; and the like

(3) Interior Ornaments:

rugs, curtains, curtain cords, tablecloths, carpets, cushions, pictureframes, imitation flowers, photo stands and the like

(4) Furnitures:

beddings such as bedclothes, pillows and mattresses; lighting fixtures;air conditioners; and the like

(5) Accessories:

rings, bracelets, tiaras, earrings, hair stoppers, artificial nails,ribbons, scarfs, watches, glasses and the like

(6) Stationeries:

writing implements, stamps, erasers, celluloid boards, rulers, adhesivetapes and the like

(7) Daily Necessaries:

cosmetics such as lipsticks, eye-shadows, manicures, hair dyes,artificial nails and paints for artificial nails; toothbrushes; and thelike

(8) Kitchen Utensils:

cups, dishes, chopsticks, spoons, forks, pots, frying pans and the like

(9) Other Products:

various printed articles, such as calendars, labels, cards, recordingmaterials and those for forgery prevention; books such as illustratedbooks; bags; packaging containers; embroidery threads; sporting gears;fishing gears; coasters; musical instruments; pocket warmers;refrigerants; pouch articles such as wallets; umbrellas; vehicles;buildings; indicators for temperature detection; training and learningarticles; and the like.

EXAMPLES

Examples of the present invention will be described below; however, thepresent invention is not restricted thereto.

The methods of producing the thermochromic color-memory composition ofthe respective Examples, the methods of producing microcapsule pigmentsencapsulating the respective compositions and the method of measuringthe discoloration temperature, as well as hysteresis characteristics,will now be described.

It is noted here that the unit “part(s)” used in the following Examplesrepresents “part(s) by mass”.

Example 1 Method of Preparing Thermochromic Color-Memory Composition

Three components composed of 1 part of3-(2-ethoxy-4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalideas the component (a), 2 parts of2,2-bis(4-hydroxyphenyl)hexafluoropropane as the component (b) and 50parts of phenoxyethyl 4-butoxybenzoate (Compound 5) as the component (c)were mixed, and the resultant was heated and uniformly dissolved toobtain thermochromic color-memory composition.

The thus obtained thermochromic color-memory composition showed adiscoloration from blue to colorless.

Preparation of Measurement Sample

The thermochromic color-memory composition was filled into a transparentglass capillary tube having an inner diameter of 1 mm and a length of 78mm up to a height of about 10 mm from the bottom of the capillary tube,thereby preparing a measurement sample.

Measurement of Discoloration Temperature

The entire part of the thus obtained measurement sample containing thethermochromic color-memory composition was immersed in a transparentheating medium. While changing the temperature of the transparentheating medium, the discoloration state of the thermochromiccolor-memory composition was visually observed, and T₁ (completecoloration temperature), T₂ (coloration on-set temperature), T₃(decoloration on-set temperature) and T₄ (complete decolorationtemperature) were measured to determine T_(H) [the middle temperaturebetween T₁ and T₂: (T₁+T₂)/2], T_(G) [the middle temperature between T₃and T₄: (T₃+T₄)/2] and ΔH (hysteresis width: T_(G)−T_(H)).

The thermochromic color-memory composition showed the followinghysteresis characteristics: T₁=14° C., T₂=18° C., T₃=57° C., T₄=61° C.,T_(H)=16° C., T_(G)=59° C. and ΔH=43° C.

Examples 2 to 6

The thermochromic color-memory compositions of Examples 2 to 6 wereprepared in the same manner as in Example 1 except that the components(a) and (c) of each thermochromic color-memory composition and theiramounts were changed as shown in the table below, and the discolorationtemperatures were also measured in the same manner as in Example 1.

TABLE 1 Component (a) Component (b) Component (c) Example Amount AmountAmount 1 P 1 part S 2 parts phenoxyethyl 4-butoxybenzoate (Compound 5)50 parts 2 Q 1 part S 2 parts phenoxyethyl 4-butoxybenzoate (Compound 5)50 parts 3 R 1 part S 2 parts phenoxyethyl 4-butoxybenzoate (Compound 5)50 parts 4 P 1 part S 2 parts phenoxyethyl 4-tetradecyloxybenzoate(Compound 42) 50 parts 5 P 1 part S 2 parts ester of phenoxyethyl4-hydroxybenzoate and 50 parts dodecanoic acid (Compound 51) stearyldecanoate 5 parts 6 P 1 part S 2 parts dodecyl ether of phenoxyethylvanillate (Compound 50 parts 40) stearyl decanoate 5 parts

In Table 1, “P” is3-(2-ethoxy-4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide;“Q” is 1,2-benz-6-(N-ethyl-N-isoamylamino)fluoran; “R” is2-(2-chloroanilino)-6-di-n-butylaminofluoran; and “S” is2,2-bis(4-hydroxyphenyl)hexafluoropropane.

The discolorations and the values of T₁, T₂, T₃, T₄, T_(H), T_(G) and ΔHof the thermochromic color-memory compositions of Examples 1 to 6 areshown in the table below.

TABLE 2 Color change: Discoloration characteristics (° C.) Examplecoloration 

 decoloration T1 T2 T3 T4 T_(H) T_(G) ΔH 1 blue 

 colorless 14 18 57 61 16 59 43 2 pink 

 colorless 16 20 55 61 18 58 40 3 black 

 colorless 16 20 55 61 18 58 40 4 blue 

 colorless 23 29 36 46 26 41 15 5 blue 

 colorless 12 14 46 60 13 53 40 6 blue 

 colorless 10 14 38 48 12 43 31

Example 7 Method of Preparing Thermochromic Color-Memory MicrocapsulePigment

Thermochromic color-memory composition composed of 1 part of3-(2-ethoxy-4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalideas the component (a), 5 parts of2,2-bis(4-hydroxyphenyl)hexafluoropropane as the component (b), 45 partsof phenoxyethyl 4-butoxybenzoate (Compound 5) and 5 parts of cetylcaprate as the component (c) was mixed and uniformly melted by heating.The resultant was further mixed with 20 parts of an aromatic polyvalentisocyanate prepolymer as a membrane wall material and 40 parts of ethylacetate, and the resulting solution was added to 100 parts of a 15%aqueous gelatin solution and emulsion-dispersed to form microdroplets.After continuously stirring the thus obtained dispersion at 70° C. forabout 1 hour, an aqueous solution obtained by dissolving 2 parts of awater-soluble amine compound (manufactured by Mitsubishi ChemicalCorporation, trade name: jER CURE U; an amine adduct of epoxy resin) in23 parts of water was slowly added thereto with stirring, and theresultant was further continuously stirred for about 3 hours with thetemperature thereof being maintained at 90° C., thereby obtainingthermochromic color-memory microcapsule pigment suspension.

From this microcapsule pigment suspension, thermochromic color-memorymicrocapsule pigment was isolated by centrifugation to obtainthermochromic color-memory microcapsule pigment showing a discolorationfrom blue to colorless (average particle size: 2.0 μm).

Preparation of Measurement Sample

Thermochromic color-memory ink composition was prepared by uniformlydispersing 40 parts of the thus obtained thermochromic color-memorymicrocapsule pigment in an aqueous ink vehicle composed of 50 parts ofan ethylene-vinyl acetate resin emulsion, 1 part of a leveling agent, 1part of an antifoaming agent, 0.5 parts of a viscosity-adjusting agentand 7.5 parts of water.

A solid pattern was screen-printed using the thus obtained inkcomposition on a high-quality paper to prepare a measurement sample.

Measurement of Discoloration Temperature

The thus obtained measurement sample was set in the measuring section ofa differential colorimeter (TC-3600 differential colorimeter,manufactured by Tokyo Denshoku Co., Ltd.). The sample portion was heatedand cooled at a rate of 2° C./min to measure the brightness as the colordensity at each temperature and a color density-temperature curve wasprepared. From this color density-temperature curve, T₁, T₂, T₃, T₄,T_(H) [the middle temperature between T₁ and T₂: (T₁+T₂)/2], T_(G) [themiddle temperature between T₃ and T₄: (T₃+T₄)/2] and ΔH (hysteresiswidth: T_(G)−T_(H)) were determined.

The thermochromic color-memory microcapsule pigment showed the followinghysteresis characteristics: T₁=−16° C., T₂=0° C., T₃=43° C., T₄=59° C.,T_(H)=−8° C., T_(G)=51° C. and ΔH=59° C.

Example 8

Thermochromic color-memory microcapsule pigment showing a discolorationfrom pink to colorless (average particle size: 1.8 μm) was prepared inthe same manner as in Example 7, except that the components (a) and (c)of the thermochromic color-memory composition encapsulated in amicrocapsule were changed to 2.0 parts of1,2-benz-6-(N-ethyl-N-isoamylamino)fluoran and a combination of 50 partsof phenoxyethyl 4-butoxybenzoate (Compound 5) and 5 parts of stearyllaurate, respectively.

The thus obtained thermochromic color-memory microcapsule pigment showedthe following hysteresis characteristics: T₁=−18° C., T₂=0° C., T₃=36°C., T₄=56° C., T_(H)=−9° C., T_(G)=46° C. and ΔH=55° C.

Example 9

Thermochromic color-memory microcapsule pigment showing a discolorationfrom blue to colorless (average particle size: 2.2 μm) was prepared inthe same manner as in Example 7, except that the component (c) of thethermochromic color-memory composition encapsulated in a microcapsulewas changed to 50 parts of phenoxyethyl 4-pentyloxybenzoate (Compound29) and 5 parts of stearyl caprate.

The thus obtained thermochromic color-memory microcapsule pigment showedthe following hysteresis characteristics: T₁=−23° C., T₂=−13° C., T₃=36°C., T₄=52° C., T_(H)=−18° C., T_(G)=44° C. and ΔH=62° C.

Application Example 1

An ink composition A was prepared by uniformly dispersing 27 parts ofthe thermochromic color-memory microcapsule pigment prepared in Example7 (which had been cooled to −16° C. or lower to develop a blue color inadvance) in a vehicle composed of 0.3 parts of succinoglycan(shear-thinning agent), 3.0 parts of a sugar mixture [manufactured bySanwa Starch Co., Ltd., trade name: SANDEC 70], 0.5 parts of aphosphate-based surfactant, 0.1 parts of an antifungal agent, 1.0 partof triethanolamine and 68.1 parts of water.

Preparation of Writing Instrument

An ink composition-storing tube composed of a polypropylene pipe wasfilled by suction with the thus obtained ink composition A and connectedvia a connection member (resin-made holder) with a ballpoint pen tipholding a 0.5-mm stainless-steel ball on its end.

Then, a viscoelastic ink follower composition (liquid plug) containingpolybutene as a main component was filled from the rear end of thepolypropylene pipe to obtain a ballpoint pen refill.

This ballpoint pen refill was incorporated into an axial barrel toobtain a writing instrument (retractable ballpoint pen).

This writing instrument had a structure in which the ballpoint penrefill was stored inside the axial barrel with a tip provided thereonbeing exposed to the outside air and the tip was projected from thefront-end opening of the axial barrel by the action of a clip-shapedprojection-retraction mechanism (sliding mechanism) arranged on the sideof the axial barrel.

On the rear end of the axial barrel, a friction member made of an SEBSresin was arranged.

With the end of the ballpoint pen tip being projected from the front-endopening of the axial barrel by the action of the projection-retractionmechanism, a blue letter (handwriting) was formed by writing on a sheetof paper.

When this handwriting was rubbed with the SEBS resin-made frictionmember arranged on the rear end of the axial barrel, the letter wasdecolored to colorless, and this state could be maintained under roomtemperature.

Meanwhile, when the sheet of paper after the decoloration was put into afreezer and cooled to a temperature of −16° C. or lower, the lettershowed a discoloration behavior of turning blue again, and this behaviorwas repeatedly reproducible.

Application Example 2

An ink composition B was prepared by uniformly dispersing 27 parts ofthe thermochromic color-memory microcapsule pigment prepared in Example7 (which had been cooled to −16° C. or lower to develop a blue color inadvance) in an aqueous ink vehicle composed of 0.33 parts of xanthan gum(shear-thinning agent), 10.0 parts of urea, 10 parts of glycerin, 0.6parts of a nonionic surfactant, 0.1 parts of a modified silicone-basedantifoaming agent, 0.2 parts of an antifungal agent and 51.77 parts ofwater.

Preparation of Writing Instrument

A polypropylene pipe was filled by suction with the thus obtained inkcomposition B and connected via a connection member (resin-made holder)with a ballpoint pen tip holding a 0.5-mm stainless-steel ball on itsend.

Then, a viscoelastic ink follower composition (liquid plug) containingpolybutene as a main component was filled from the rear end of thepolypropylene pipe and a tail plug was fitted to the rear of the pipe.Further, a front axial barrel and a rear axial barrel were assembledthereto and a cap was fitted to prepare a writing instrument (ballpointpen).

On the back of the rear axial barrel, a friction member made of an SEBSresin was arranged.

Using the thus obtained writing instrument, a blue letter (handwriting)was formed by writing on a sheet of paper.

This handwriting showed a blue color at room temperature (25° C.) and,when the letter was rubbed with the friction member, the letter wasdecolored to colorless and this state could be maintained under roomtemperature.

Meanwhile, when the sheet of paper after the decoloration was put into afreezer and cooled to a temperature of −16° C. or lower, the lettershowed a discoloration behavior of turning blue again, and this behaviorwas repeatedly reproducible.

Application Example 3

An ink composition C was prepared by mixing 25 parts of thethermochromic color-memory microcapsule pigment prepared in Example 8(which had been cooled to −18° C. or lower to develop a pink color inadvance) with 0.5 parts of hydroxyethyl cellulose, 0.2 parts of acomb-type polymeric dispersant [manufactured by Lubrizol Japan Ltd.,trade name: SOLSPERSE 43000], 1.0 part of an organic nitrogen sulfurcompound [manufactured by Hokko Chemical Industry Co., Ltd., trade name:HOKUSIDE R-150, a mixture of 2-methyl-4-isothiazolin-3-one and5-chloro-2-methyl-4-isothiazolin-3-one], 0.5 parts of polyvinyl alcohol,25.0 parts of glycerin, 0.02 parts of an antifoaming agent and 47.78parts of water.

Preparation of Filled-In Type Writing Instrument

An ink composition absorbent prepared by covering a polyester sliverwith a synthetic resin film was impregnated with the thus obtained inkcomposition C and inserted into an axial barrel made of a polypropyleneresin. Then, the axial barrel was assembled with a resin-processed penbody (cannonball shape) made of polyester fibers via a connection memberin such a manner that the front end of the axial barrel was in contactwith the pen body, and a cap was fitted thereto to obtain a writinginstrument (marking pen).

On the rear end of the axial barrel, a friction member made of an SEBSresin was fitted.

Using the thus obtained writing instrument, a pink letter (handwriting)was formed by writing on a sheet of paper.

This handwriting showed a pink color at room temperature (25° C.) and,when the letter was rubbed with the friction member, the letter wasdecolored to colorless and this state could be maintained under roomtemperature.

Meanwhile, when the sheet of paper after the decoloration was put into afreezer and cooled to a temperature of −18° C. or lower, the lettershowed a discoloration behavior of turning pink again, and this behaviorwas repeatedly reproducible.

Application Example 4

A paint D was prepared by dispersing 2.5 parts of the thermochromiccolor-memory microcapsule pigment prepared in Example 7 and 1.5 parts ofa non-thermochromic fluorescent pink pigment in an oil-based ink vehiclecomposed of 12.5 parts of a vinyl chloride-vinyl acetate copolymerresin, 38.3 parts of xylene, 45 parts of butyl acetate and 0.2 parts ofa viscosity-adjusting agent.

After allowing the thus obtained paint D to change its color to purpleby cooling it to a temperature of −16° C. or lower, the paint wasspray-coated on a plug part (white) of a household electric cord to forma reversibly thermochromic layer, thereby obtaining thermochromiccolor-memory plug.

This plug showed a purple color at room temperature (25° C.); however,when heated, it turned pink at a temperature of 59° C. or higher. Whenthe plug was cooled from this discolored state, it again showed a purplecolor at a temperature of −16° C. or lower.

Once this thermochromic color-memory plug turns pink at a temperature of59° C. or higher, it is capable of maintaining a discolored state inpink unless it is cooled to a temperature of −16° C. or lower. Thisenabled to visually detect the temperature history when the plug wasabnormally overheated and reached a high-temperature range of 59° C. orhigher.

Application Example 5

An ink composition E was prepared by uniformly dispersing 30 parts ofthe thermochromic color-memory microcapsule pigment prepared in Example7 (which had been cooled to −16° C. or lower to develop a blue color inadvance) in an aqueous ink vehicle composed of 60 parts of an acrylicresin emulsion (solid content: 45%), 1 part of a viscosity-adjustingagent, 0.2 parts of an antifoaming agent and 8.8 parts of water.

Using the thus obtained ink composition E, a large number of starpatterns were screen-printed on a white T-shirt (made of cotton) with a100-mesh screen plate to obtain thermochromic color-memory T-shirt.

On this T-shirt, a large number of blue star patterns were visuallyrecognized at room temperature (25° C.) and the star patterns were notchanged by the body temperature or ambient temperature; however, whenthe T-shirt was heated to 59° C. or higher, the star patterns turnedcolorless, and they were again visually recognized when the T-shirt wascooled to −16° C. or lower.

It was possible to arbitrarily change the design of the T-shirt bydecoloring some of the star patterns with heating the T-shirt using aniron or the like to decolor only arbitrary stars or to form letters orpatterns with arbitrary stars.

Further, the T-shirt was able to retain such a discolored state in aroom temperature range, and an arbitrary design could be again formed asdescribed above by heating the whole T-shirt to 59° C. or higher todecolor all of the star patterns and then cooling the T-shirt to −16° C.or lower to allow all of the stars to show the color.

Application Example 6

Using an extruder, 5 parts of the thermochromic color-memorymicrocapsule pigment prepared in Example 8, 1 part of a dispersant, 0.1parts of a non-thermochromic blue pigment and 93.9 parts of apolypropylene homopolymer were melt-mixed at 180° C. to obtain a pelletF.

From the thus obtained pellet F, a grape-shaped ornament article wasmolded using an injection molding machine.

After being cooled to −18° C. or lower, this ornament article showed apurple color at room temperature (25° C.); however, the ornament articleshowed a blue color when heated to a temperature of 56° C. or higher.When the ornament article was cooled from this state, it again showed apurple color at a temperature of −18° C. or lower.

Application Example 7

An ink composition G was prepared by uniformly dispersing 20 parts ofthe thermochromic color-memory microcapsule pigment prepared in Example9 (which had been cooled to −23° C. or lower to develop a blue color inadvance) in an aqueous ink vehicle composed of 78.0 parts of an acrylicresin emulsion (solid content: 40%) and 2.0 parts of an antifoamingagent.

Using the thus obtained ink composition G, a forgery detection mark wasgravure-printed on a gift certificate printed with a non-thermochromicink on a high-quality paper.

This forgery detection mark showed a blue color at room temperature (25°C.) and its color was not changed by the body temperature or ambienttemperature; however, the mark turned colorless when heated to 52° C. orhigher, and the mark again showed a blue color when cooled to 23° C. orlower.

Since this forgery detection mark of the gift certificate shows a bluecolor and does not change its color in a room temperature range, itcannot be discriminated as a forgery detection mark; however, the markturns colorless when heated to 52° C. or higher and thus has aforgery-preventing function.

DESCRIPTION OF SYMBOLS

-   -   T₁: complete coloration temperature    -   T₂: coloration on-set temperature    -   T₃: decoloration on-set temperature    -   T₄: complete decoloration temperature    -   ΔH: hysteresis width

1. Thermochromic color-memory composition comprising: (a) a componentcomposed of an electron-donating color-developing organic compound; (b)a component composed of an electron-accepting compound; and (c) acomponent composed of an ester compound represented by the followingFormula (1) as a reaction medium which controls color reaction betweensaid components (a) and (b):

(wherein, R represents an alkyl group having 3 to 18 carbon atoms or analiphatic acyl group having 3 to 18 carbon atoms; X represents ahydrogen atom, an alkyl group having 1 to 3 carbon atoms, an alkoxygroup having 1 or 2 carbon atoms or a halogen atom; Y represents ahydrogen atom or a methyl group; and Z represents a hydrogen atom, analkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 or 2carbon atoms or a halogen atom).
 2. The composition according to claim1, wherein, in said ester compound represented by said Formula (1), saidR represents an alkyl group having 4 to 14 carbon atoms or an aliphaticacyl group having 6 to 16 carbon atoms; said X represents a hydrogenatom, a methyl group or a methoxy group; said Y represents a hydrogenatom; and said Z represents a hydrogen atom, a methyl group or a methoxygroup.
 3. The composition according to claim 1, wherein said component(a) is a compound selected from the group consisting of phthalidecompounds, fluoran compounds, styrynoquinoline compounds, diazarhodaminelactone compounds, pyridine compounds, quinazoline compounds andbisquinazoline compounds.
 4. The composition according to claim 1, whichhas a hysteresis width (ΔH) of 8° C. to 80° C.
 5. Thermochromiccolor-memory microcapsule pigment encapsulating the compositionaccording to claim
 1. 6. Ink composition comprising: the microcapsulepigment according to claim 5; and a vehicle.
 7. Writing instrumentcomprising: an axial barrel which stores the ink composition accordingto claim 6; and a pen body which delivers said ink composition stored insaid axial barrel.
 8. The writing instrument according to claim 7,further comprising a friction member.
 9. Writing instrument setcomprising: the writing instrument according to claim 7; and a frictionbody.
 10. The composition according to claim 2, wherein said component(a) is a compound selected from the group consisting of phthalidecompounds, fluoran compounds, styrynoquinoline compounds, diazarhodaminelactone compounds, pyridine compounds, quinazoline compounds andbisquinazoline compounds.
 11. The composition according to claim 2,which has a hysteresis width (ΔH) of 8° C. to 80° C.
 12. The compositionaccording to claim 3, which has a hysteresis width (ΔH) of 8° C. to 80°C.
 13. Thermochromic color-memory microcapsule pigment encapsulating thecomposition according to claim
 2. 14. Thermochromic color-memorymicrocapsule pigment encapsulating the composition according to claim 3.15. Thermochromic color-memory microcapsule pigment encapsulating thecomposition according to claim
 4. 16. Writing instrument set comprising:the writing instrument according to claim 8; and a friction body.